/f  li  j; 


U 


DEPOSITORY 


B     P     l       397 


*-*•*<* 


United  States  Department  of  Agriculture, 

BUREAU  OF  PLANT  INDUSTRY— Circular  No.  14. 

B.  T.  GALLOWAY,  Chief  of  Bureau. 


CHANGE  OF  VEGETATION  ON  THE  SOUTH  TEXAS  PRAIRIES. 

By  O.  I'.  Cook, 
Bionomisi  in  Charge  of  Bionomic  Investigations  of  Tropical  and  Subtropical 

Plants. 


It  is  a  matter  «> f  popular  knowledge  in  south  Texas  ihai  extensive 
regions  which  were  formerly  grassy,  open  prairies  are  now  covered 
with  a  dense  growth  of  mesquite  (Prosopis),  prickly-pear  cactus 
(Opuntia),  and   many  other  shrubby   plants  of   intermediate   size. 

Testimony  to  this  effect  is  definite  and  unanimous.  It  differs  locally 
only  in  the  number  of  years  since  the  bushes  began  to  grow  thirty 
years,  or  twenty,  or  ten  subsequent  to  the  establishment  of  the  rrra/. 
ing  industry  on  a  Large  scale,  the  annual  burning  of  the  grass  by 
ili''  cattlemen,  and  finally  the  fencing  of  the  land  for  >till  more 
intensive  grazing. 

Many  localities  are  only  now  being  invaded  by  the  woody  vegeta- 
tion. Very  often  the  old  mesquite  pioneers,  the  scattered  tree-  which 
made  the  "open  mesquite  country"  of  other  decades,  are  -till  con- 
spicuous among  their  much  smaller  progeny  and  tin-  crowd-  of 
other  camp-following  species  which  now  occupy  the  land  to  the 
almost  complete  exclusion  of  the  grasses  upon  which  the  herds  of 
former  days   were   pastured.      A    new    order  of  nature   is  at    hand   in 

south  Texas.     The  change  ha-  c e  so  gradually   that   even   those 

who  have  the  most   intimate  acquaintance  with  the   fact-  have  not 
appreciated  their  significance,  much  less  published  them  abroad. 

Before  the  prairie-  were  grazed  by  cattle  the  luxuriant  growths  of 
grass  could  accumulate  for  several  years  until  condition-  were  favor 
able  for  accidental  fires  t<>  spread.     With  these  large  supplies  of  fuel 
the  lire-  which  swept  over  these  prairie-  were  very  besoms  of  de 
struction  not  only  for  man  and  animal-  hut  for  all  shrubs  and  trees 


54116     cir.lt     us 


2  CHANGE    OF   VEGETATION    ON    SOUTH    TEXAS    PRAIRIES. 

which  might  have  ventured  out  among  the  grass,  and  even  for  any 
trees  or  forests  against  which  the  burning  wind  might  blow. 

That  such  fires  were  evidently  the  cause  of  the  former  treeless 
condition  of  the  southwestern  prairies  is  also  shown  by  the  fact  that 
trees  are  found  in  all  situations  which  afford  protection  against  fires. 
Along  beaches  and  on  naked  sand  dunes,  in  grassless  river  bottoms 
and  abandoned  channels  of  "  slews,"  in  deep  swamps  and  in  sterile 
rocky  jDlaces  the  forest  has  maintained  footholds.  Nor  is  there  any 
reason  in  the  nature  of  the  climate  or  the  soil  why  trees  should  not 
thrive  over  the  vast  areas  of  open  prairie  land.  Trees  of  many  kinds 
have  thriven  well  where  planted  in  villages  and  about  homesteads,  in 
addition  to  the  natural  spread  of  the  woody  vegetation  as  soon  as 
the  fires  cease. 

Those  who  are  acquainted  only  with  northern  regions  of  hills  and 
valleys,  heavy  rains,  and  deep  snows  may  find  it  difficult  to  believe 
that  the  burning  of  grass  can  destroy  or  prevent  the  growth  of  forests 
and  keep  vast  regions  in  a  treeless  condition.  One  needs,  perhaps,  to 
have  the  mind  prepared  by  actual  observation  of  the  destruction  of 
forests  by  fires  of  grass.  In  humid  countries  dead  grass  is  beaten 
down  and  decays  during  the  next  summer  season.  Forest  fires  in 
northern  countries  arise  from  accumulations  of  fallen  leaves  and 
other  debris,  but  in  the  warmer  parts  of  the  world  these  conditions 
are  generally  reversed.  The  forests  do  not  burn  with  their  own 
fuel,  but  may  be  invaded  and  driven  back  by  the  adjacent  grass.  In 
this  respect,  as  in  several  others,  south  Texas  may  be  reckoned  as  a 
part  of  the  Tropics,  in  spite  of  the  occasional  "  northers  "  of  the 
winter  season,  which  carry  the  temperature  below  the  freezing  point 
and  thus  exclude  all  the  tender  tropical  types  of  perennial  plants. 

The  traveler  in  Mexico  and  Central  America  encounters  many 
illustrations  of  the  advantage  enjoyed  by  grasses  over  other  vegeta- 
tion in  the  presence  of  fire.  Large  areas  of  land  formerly  cultivated 
by  the  native  Indians  remain  barren  of  everything  except  the  coarse 
grasses  which  afford  the  fuel  of  the  fires  that  prevent  the  growth  of 
trees  and  the  renewing  of  the  soil.  In  regions  not  subject  to  such 
fires  the  forest  is  rapidly  renewed  and  the  land  can  be  cleared  and 
planted  again  at  intervals  of  a  few  years. 

Even  where  the  grass-grown  land  has  not  been  cleared  by  man  it 
is  possible  for  wild  grasses  to  drive  back  adjacent  forests  with  the 
aid  of  fire.  In  this  way  a  species  of  wire  grass  (Epicampes)  is  de- 
stroying forests  of  alders  and  pines  on  the  upper  slopes  of  the  Vulcan 
de  Agua  in  Guatemala.  Before  the  access  of  fires  this  grass  appears 
to  have  been  confined  to  the  crater  and  to  the  vevy  dry  upper  slopes 
where  the  pine  trees  are  small  and  scattering.  Now  that  the  belts 
of  humid  forests  lower  down  have  been  broken  by  clearings  the  grass 

[Cir.  M  I 


CHANG]     OF    VEG1   I  \  1  I  -  >  n    on    SOUTH    TEXAS    1*1:  \  I  K  ,1 

has  the  assistance  of  fire  and  is  destroying  the  larger  growth  with 
increasing  rapidity . 

There  are  no  springs  or  streams  on  the  upper  slopes  of  the  volcano, 
so  thai  the  grass  is  not  pastured.  It-  long  wiry  stems  and  leaves 
accumulate  until  there  are  quantities  of  fuel  sufficient  to  kill  large 
trees  and  to  drive  back  the  forest  for  long  distances  at  each  confla- 
gration." The  lower  the  grass  comes  the  more  luxuriant  its  growth 
and  ilic  more  destructive  the  next  fire.  This  will  continue  as  long 
as  the  grass  is  ungrazed  or  care  is  not  taken  to  burn  it  every  year  in 
order  to  prevent  the  accumulation  of  dangerous  quantities  of  fuel. 

Settlers  in  south  Texas  early  adopted  the  practice  of  burning  over 
the  prairies  everj  year;  partly  to  protect  their  homes  against  the  fires, 
partly  to  give  their  cattle  readier  a<  cess  to  the  fresh  growth  of  grass. 
The  fires  were  often  set  near  the  coast,  the  strong  breeze  which  blows 
in  from  the  Gulf  spreading  the  flames  over  many  square  miles. 
While  the  grass  was  -till  abundant  these  annual  burnings  were  able  to 
keep  the  woody  vegetation  well  in  check,  though  no  longer  able  to 
drive  ba<  k  the  forest  or  even  to  prevent  a  slow  advance. 

In  spots  where  the  grass  IS  thin,  seedling  mesquites  and  oaks  es- 
cape the  flames  and  iii  a  year  or  two  begin  to  -hade  the  ground  and 
gain  more  protection  against  the  dangerous  proximity  of  the  combus- 
tible grass;  and  even  though  the  tops  are  killed  by  later  fires  the  roots 
may  send  up  sprouts  again  and  again  to  improve  cm  ry  chance  id'  be- 
coming established  and  joining  branches  with  near  neighbors  to  in- 
crease the  area  of  shade.  The  lessened  quantity  of  grass  also  makes 
n  impracticable  to  burn  the  prairies  over  in  the  summer,  as  was  cus- 
tomary in  former  decade-.  Burning  ha-  now  to  he  done  in  the  winter 
when  the  grass  is  dry,  but  the  young  tree-  are  then  in  a  dormant  con- 
dition and  are  much  less  injured  by  the  (ire  than  in  the  summer  season 
of  vegetative  activity . 

In  the  region  between  Houston  ami  Victoria  large  tract-  are  being 
occupied  l>\  "oak  runner-."  Farther  south,  the  mesquite  usually 
held  -way  alone  for  a  considerable  period  before  the  -mailer  and 
less  hardy  type-  were  able  to  advance  against  the  gradually  weaker 
lire-.     W'iih  the  building  of  barbed-wire  fence-  and  the  provision  of 

iii"  roots  of  iliis  grass  are  well  protected  from  the  Sre  by  mas-.-.  of  the 
closely  packed  siems.  These  tufts  remain  wet  while  everything  else  is  thor- 
oughly dried.  Excepl  in  rainy  weather  lie  water  can  he  obtained  from  the 
extremely  coarse  and  loose  volcanic  ashes  ami  rocks  of  which  the  upper  parts 
■  ■I'  the  mountain  an-  composed.     Weldenia  ami  other  native  plants  show  strik- 

[ng  adaptations  for  drought  resistance.     Even  the  alder  has  a  r arkably  thick. 

cheess  hark.  whi«h  doubtless  serves  for  the  storage  of  additional  supplies  ■■ 
water. 

''  It    is  also  pointed  ou1   by   Mr.   Frederick   v.  Coville  thai    the  young  w ly 

plants  musl   In'  able  in  make  mure  rapid  growtb  than   formerly  because  of  the 
reduced  competition  of  the  grasses  for  the  moisture  of  the  soil. 
ni 


4  CHANGE    OF    VEGETATION    ON    SOUTH    TEXAS    PRAIRIES. 

permanent  supplies  of  water  by  wells  and  reservoirs  the  cattle  were 
greatly  increased.  About  a  decade  ago  there  was  a  series  of  very 
dry  seasons  when  the  cattle  left  little  grass  to  burn,  often  none  at 
all.  This  was  a  time  of  notable  prosperity  for  the  bushes  and  cacti. 
Through  many  square  miles  of  the  Rio  Grande  Valley,  and  doubtless 
in  many  other  parts,  the  victory  over  the  grass  was  complete  and  final. 
There  has  been  no  burning  since,  nor  ever  will  be,  unless  the  bushes 
grow  thick  and  accumulate  dry  wood  enough  to  furnish  the  fuel. 

The  mesquite  alone  worked  little  injury  to  the  grazing  industry. 
for  the  pods  are  relished  by  cattle  and  horses,  supplementing  the 
otherwise  exclusive  diet  of  grass  and  affording  a  reserve  supply  of 
food  in  dry  seasons.  When,  however,  the  huisach  (Acacia  farnesi- 
ana)  and  smaller  shrubs  and  cacti  become  numerous  enough  to  kill 
out  the  grass,  the  pasturage  rapidly  diminishes.  The  ranch  owner 
then  encounters  the  problem  of  clearing  his  pastures  anew  at  much 
expense  of  labor  and  time  or  of  selling  the  more  fertile  lands  in  small 
areas  to  the  truck  farmers  who  are  now  finding  in  south  Texas  a 
field  of  very  remunerative  labor.  The  warmth  of  the  early  spring 
months  enables  them  to  market  their  products  while  prices  are  still 
very  high.  This  movement  toward  more  intensive  agriculture  in 
south  Texas  is  carrying  with  it  the  building  of  railroads  and  the  con- 
struction of  extensive  facilities  for  irrigation.  In  the  Kingsville  and 
Falfurrias  districts  water  is  being  developed  by  artesian  wells;  in 
the  Rio  Grande  Valley  by  pumping  from  the  river. 

South  Texas  was  occupied  until  recently  by  a  few  cattle  ranches, 
larger  than  many  counties  of  our  Northern  States  and  managed  in 
truly  feudal  fashion  by  widely  scattered  communities  of  Spanish- 
speaking  retainers.  Formerly  there  was  no  welcome  for  the  crop- 
raising  farmer,  but  now  buyers  of  small  tracts  are  in  demand.  South 
Texas  is  being  rushed  under  the  plow  to  escape  the  invasion  of 
bushes.  Large  tracts  which  could  have  been  bought  a  few  years  ago 
for  a  dollar  or  less  per  acre  and  could  then  have  been  put  under 
cultivation  without  other  expense  than  the  plowing  and  sowing, 
now  cost  $5  or  $10  an  acre  to  clear  of  woody  growth,  in 
addition  to  the  greatly  increased  prices  of  the  land  itself.  But  in 
the  region  to  the  north  of  Brownsville  many  thousands  of  acres  are 
already  lost,  at  least  to  the  present  generation,  for  the  bushes  are  so 
well  intrenched  that  the  cost  of  clearing  would  greatly  exceed  the 
value  of  the  land. 

This  shrubby  vegetation  which  is  threatening  the  cattle  industry 
and  opening  south  Texas  to  the  truck  and  cotton  farmers  will 
undoubtedly  continue  to  advance  and  multiply  wherever  the  land  is 
not  cleared  and  cultivated.  The  south  Texas  fanner  of  the  future  in- 
stead of  being  a  cattle  king  may  even  find  himself  without  a  place  to 
pasture  his  milch  cows  except  in  his  tilled  fields. 

[Cir.  14] 


CHANGE   OF    \  i  Gl   LATION    OH    SOI    Ml     CEXAS    PRAIR]  5 

The  botanical  explorers  who  have  associated  the  South  Texas 
region  with  the  deserts  farther  to  the  wesl  because  they  found  it 
occupied  by  the  same  desert  types  of  vegetation  must  revise  their  con- 
clusions in  the  lighl  of  facts  alreadj  accomplished  and  of  others  not 
long  to  be  delayed.  The mesquites, cacti, chaparral,  and  sagebrush 
only  an  episode  of  the  bionomic  history  of  the  region,  not  it-  original 
or  norma]  condition  or  an  index  of  its  agricultural  possibilities.  They 
are  merely  the  forerunners  of  the  larger  forest  growth.  If  reforesta- 
tion were  to  continue  uninterrupted  by  fires  or  other  forms  of  human 
interference  the  Gulf  plains  of  Texas  would  again  become  covered 
with  dense  subtropical  forests,  and  with  the  then  impeded  drainage 
would  form  vast  swamps,  such  as  doubtless  existed  before  the  advenl 
of  agricultural  man.  as  shown  by  the  now  isolated  remnants  of  the 
earlier  forests. 

The  primitive  Indian  agriculture  which  accomplished  the  devasta- 
tion of  this  region  as  of  many  others  in  Mexico  and  Central  America 
was  here,  as  elewhere,  a  self-limiting  process.  Lands  once  cleared  and 
abandoned  were  kepi  by  the  lire-  from  becoming  reforested  until  the 
forests  were  all  gone.  That  age  of  primitive  agriculture  ended  in  an 
age  of  grass  and  prairie  fires,  of  wandering  buffaloes,  and  nomadic 
hunter-. 

European  settlers  brought  in  the  age  of  cattle,  of  diminishing 
quantities  of  grass,  of  weaker  fires  and  advancing  bushes,  the  pioneers 
of  a  new  conquest  by  the  forests.  But  the  forests  and  swamps  will  not 
be  permitted  to  return,  for  south  Texas  is  being  plowed  and  planted. 
A  new  chapter  in  the  history  of  agricultural  development  is  being 
opened.  The  age  of  farm-,  wells,  canals,  and  railroad-  is  at  hand. 
Towns  and  cities  are  springing  up,  confidenl  of  a  future  of  prosperity 
based  on  the  immense  fertility  of  this  mosl  recent  extension  of  the 
already  vast  agricultural  empire  of  Texas. 

Though  the  long  summer  seasons  are  more  truly  tropical  than  many 
regions  which  lie  within  the  Torrid  Zone,  it  should  not  be  supposed 
that  south  Texas  is  hotter  in  the  summer  or  less  comfortable  to  live 
in  than  the  other  parts  of  the  State.  The  daily  breezes  from  the  Gulf 
moderate  the  extremes  of  heat  and  humidity  often  encountered  farther 
north. 

The  climate  t>(  the  southern  coast  belt  also  differs  notably  from  that 
of  the  drier  interior  behind  it.  where  true  desert  conditions  prevail, 
suited  to  tin'  date  palm,  like  part-  of  V.rizona  and  southern  Cali- 
fornia,      hale    palm-    thrive    and    ripen    their    fruit-    at     Laredo.    Rio 

1  The  Texas  palmetto  (Inodcs  tt  xana  i.  whicb  now  sinus  to  he  closely  confined 
to  the  banks  of  the  lower  Kin  Grande,  appears  in  have  extended  formerly  over 
two  hundred  miles  farther  north.  Tall  palmettos  were  seen  in  Jackson  Couuty 
as  late  as  tsTc,  by  Mr.  J.  1  >.  Mitchell,  of  Victoria. 

I  fir    1  |  ] 


b  CHANGE    OF   VEGETATION    ON    SOUTH    TEXAS    PRAIRIES. 

Grande  City,  and  Falfurrias,  and  may  become  one  of  the  agricultural 

resources  of  the  intervening  region.  The  warmer  spring  season  of 
south  Texas  enables  the  palms  to  flower  earlier  than  in  southeastern 
California,  which  compensates  for  lower  temperatures  later  in  the 
season. 

The  same  qualities  of  soil  which  have  produced  desert  conditions 
by  making  the  land  relatively  impervious  to  water  while  uncultivated 
now  render  it  extremely  retentive  of  moisture  under  tillage.  The 
sand  which  has  drifted  in  from  the  Gulf  and  covered  extensive  tracts 
in  the  region  south  of  Kingsville  and  Falfurrias  often  serves  the  use- 
ful purpose  of  a  mulch.  The  rain  is  absorbed  and  has  time  to  soak 
into  the  tenacious  subsoil,  and  is  there  preserved  from  evaporation. 
The  presence  of  small,  delicate  types  of  soil-inhabiting  animals 
(scolopendrella,  campodea,  japyx,  etc.)  shows  that  these  more  sandy 
prairies  of  south  Texas  are  able  to  retain  permanent  supplies  of 
moisture  instead  of  being  subject  to  the  complete  drying  out  which 
precludes  the  existence  of  such  creatures  in  many  of  the  more  northern 
parts  of  the  State. 

The  effect  of  tillage  on  the  retention  of  moisture  in  the  soil  is  also 
shown  sometimes  in  a  very  striking  manner.  Digging  in  the  undis- 
turbed soil  of  the  prairie  under  the  grass  or  among  the  desert  shrubs 
may  find  the  soil  dry  and  hard,  with  no  evidence  of  moisture  within 
the  range  of  the  roots  of  crops.  A  few  rods  away  where  land  of  the 
same  kind  has  been  cleared  and  tilled,  digging  shows  a  loam-like  sub- 
soil, darkened  with  moisture  that  can  almost  be  squeezed  out  with  the 
hand,  though  no  rain  may  have  fallen  for  many  weeks. 

It  may  be  that  in  south  Texas  dry  farming  will  be  reduced  eventu- 
ally to  an  exact  system,  for  it  will  be  possible  with  modern  scientific 
appliances  to  measure  the  water  in  the  ground  almost  as  accurately 
as  if  it  were  stored  in  tanks  or  reservoirs.  The  farmer  can  with- 
hold his  seed  till  he  has  water  enough  and  may  become  less  dependent 
upon  the  vicissitudes  of  the  weather  than  in  regions  where  soils  are 
less  retentive  and  plants  must  have  rain  during  the  growing  season. 
Excellent  crops,  especially  of  cotton,  are  often  raised  in  south  Texas 
from  this  earth-stored  moisture  alone  without  any  rain  or  irrigation 
during  the  growing  season.  The  dryness  of  the  air  and  of  the  surface 
-oil  precludes  serious  injury  from  the  boll  weevil,  giving  this  region 
an  important  advantage  over  the  more  humid  parts  of  the  cotton  belt. 

Land-hungry  thousands  who  have  not  been  satislied  in  Oklahoma. 
Kansas,  or  the  Dakotas  are  now  hearing  of  the  attractions  of  south 
Texas,  and  are  arriving  by  trainloads  to  spy  out  the  land.  Unfortu- 
nate speculations  and  "  booms  "  and  many  individual  losses  and  dis- 
appointments will  doubtless  mark  the  history  of  this  as  of  other 
newly  occupied  region-  of  the  Wesl .  but  the  fact  will  remain  that 
[Cir.  14] 


CHANG]     OF    \n;i   i'\i'|o\    ON    SOUTB     i  I  \  VS    PRATRT]  7 

there  is  fertile  -nil  and  thai  crops  of  manj  kinds  can  be  raised,  in 
winter  as  well  as  in  summer,  whenever  there  is  water  enough  to  en- 
able them  to  gro^  i al  urn  \ . 

A  J  i|  n  <  >\  ed  : 

James  \\ H  son, 

Si '  ii  fa ri/  of  .  Agriculture. 

Washington,  I).  ('..  .1  ugusi  /.'.  19 

[CIr    I  I  1 

o 


UNIVERSITY  OF  FLORIDA 


3  1262  08928  9697 


